FR2489295A1 - METHOD AND APPARATUS FOR PREHEATING PULVERULENT MATERIALS BEFORE THEY ARE INTRODUCED IN A FUSION OVEN - Google Patents

Abstract

THE PROCESS AND THE APPARATUS ACCORDING TO THE PRESENT INVENTION IMPROVE THE PREHEATING OF PULVERULENT MATERIALS, THEIR INTRODUCTION IN FUSION FURNACES AND THEIR MIXING IN THE LATTER. THE PREHEATING IS CARRIED OUT WITH THE AID OF A PREHEATER 11 IN WHICH THE PULVERULENT MATERIALS ARE INTRODUCED AS WELL AS A FRACTION OF THE PULVERULENT MATERIALS HEATED BY A VALVE 22 AND RECYCLED IN THE PREHEATER BY THE INTERMEDOR 32. PULVERULENT MATERIALS ARE HEATED DURING THEIR PASSAGE THROUGH TUBES 17 AROUND WHICH VERY HOT LOST GAS CIRCULATES. APPLICATION: AMONG OTHERS, FUSION OF GLASS.

Description

Process and apparatus for preheating powdery materials before

  their introduction into a melting furnace Various types of manufacturing processes are known in which the starting materials are introduced into the furnace while they are cold or at ambient temperature using devices operating either continuously or in a continuous manner.

  batchwise. These devices are often protected by a

  hydraulic cooling coil or any other type that absorbs heat from the oven and further intensifies the cooling of the materials introduced into this oven. In these processes, the starting materials are subjected to heating only after they have been introduced into the furnace, where they receive, at a high temperature, the quantities of heat which are necessary to heat them, in order to ensure completion of endothermic reactions, and for

  provide them with sufficient fluidity to guarantee the home

  genesis and refinement of the resulting molten glass mass.

  It has been observed in the manufacture of glass that the most important part of the heat supplied to the starting materials serves to increase the temperature of these materials rather than to generate reactions. In most known processes, the starting materials are deposited on the top of the melt and subjected to the radiation of flames flowing with great turbulence over these materials. Since newly introduced materials are not good heat conductors, heat exchange is poor, slowing the

merger process.

  The present invention is particularly concerned with

  performance and production rate of the

  It provides a means of operating a glass melting furnace in a continuous and uniform manner at or beyond full capacity, if desired. The apparatus is adapted to preheat fully mixed glass forming ingredients before these ingredients are sent to the melting furnace, and preferably using for this preheating of the vitrifiable mixture the heat of the lost gases from the melting furnace, and continuously passing the batch through the preheater to the melting furnace. The present invention relates to a method and a means for

  the objects mentioned above.

  above and to make a device for preheating the

  vitrifiable mixture and for the use of lost gases

  furnace for melting glass, or air pre-

  heated very hot from these ovens, as it will appear

  in more detail in the description which follows.

  The preheater for the vitrifiable mixture makes it possible to use, for the heating of this element, the heat of the

  lost gas from the smelting furnace, which otherwise escapes

  drown in the atmosphere by the chimney. Although the use

  very hot lost gases is preferable for operating

  The preheater, the preheated air that comes from the furnace areas, is the "stack for heat recovery and is used for combustion, or an additional heat source such as an oil burner or The gas, alone or in combination, may be used to heat the air or waste gases intended for the operation of the preheater, or the atmospheric air may be heated to operate the batch preheater. continuous batch batch at a predetermined elevated temperature and suitable for an oven that is used for either continuous or batch operations, allows more even operation of the furnace with a notable increase in efficiency and capacity of the furnace.

oven production.

  There is a considerable number of US patents

  which deal with the initial preheating of the vitreous mixture

  reliable before it is introduced into the melting furnace. US Patent No. 3,607,170 discloses a method and apparatus in which the batch is preheated in a non-oxidizing atmosphere while being advanced in a given direction through a preheat zone of a tunnel furnace. A mixture of glass powder and a foaming agent is discharged into a hopper comprising a series of

through which the mixture passes.

  US Pat. No. 3,172,648 describes a preheating of pulverulent materials in which all the fumes of the

  preheating zone are in direct contact with the

  used to form the glass, this contact causing the entrainment of dust in the fumes emitted. US Pat. No. 4,045,197 relates to an apparatus and a method for recovering waste heat from gases.

  exhaust of a glass melting furnace and for the

  by means of heat pipes to an enclosure in which the materials of the incoming glass batch are preheated before being transferred to an oven for their

  fusion. The heat pipes contain sodium metal-

as a fluid coolant.

  US Pat. No. 3,788,832 and US Pat. No. 3,880,639 both concern the preheating of the agglomerated materials of a vitrifiable mixture by direct contact with an effluent.

  gas escaping from an oven for melting the glass.

  US Pat. No. 3,185,554 relates to a method for pre-

  to heat the materials of a vitrifiable mixture by independent heating means other than the effluent so that there is no unpredictable relationship between the varying amounts of waste heat and the amount of heat used

  to preheat the unmelted materials of the vitreous mixture

reliable.

  A considerable number of other patents relate to direct heat exchange between incoming materials of a

  batch and exhaust gases from a glass melting furnace.

  These patents are 3,607,190, 4,026,691, 3,526,492, 3,350,213, 1,543,770, 3,753,743, 1,610,377 and 4,099,953. direct and indirect heat exchange between very hot exhaust gases from a glass melting furnace and the materials of the incoming batch mixture; however, none can achieve the results that can be achieved

in accordance with the present invention.

  The present invention will now be described with reference to the accompanying drawings, in which: FIG. 1 is a partially cut-away perspective view of the vitrifiable batch preheating apparatus for implementing the present invention; FIG. in enlarged partial vertical section of the preheater shown in FIG.

  Referring to the drawings, we see that we have

  schematically in FIG. 1p a glass melting furnace 10 of the regenerating type epeaut nme base or sole refractory bricks, on which bone deposits the ingredients for the formation of the glass bathG gas and air are

  normally mixed and burned in the oven above the

  for the formation of glass2 and the resultant heat melts the mixed materials into a mass of molten glass, which is supplied or shaped at one end to

  following a refining. Rooms or passages of regeneration

  Heat accumulation or accumulation is normally located below the melting chamber of the furnace. The gas and air usually pass through the passages.

  regeneration below the oven floor for a pre-treatment

  heating and through side openings that open into the furnace's melting chamber where they are burnt so

  to melt glass forming materials. The gases

  Very hot charges then pass through opposite side ports and then through the regeneration passages for heat recovery and then reach flue ducts and a discharge stack. After a limited period of operation in this manner, the path of the gases and the incoming air is switched, using appropriate registers and timing means, so that the combustible gases then enter the chamber. melting through opposite ports, the very hot lost gases then passing through passages and flue ducts opposite to the chimney. Due to the alternate use of the regeneration passages for the incoming fuel and for the very hot outgoing lost gases, the incoming fuel is preheated

  by the bricks of the regeneration passages that were heated

  by flue gases that escape and have passed through

  previously these passages. The whole of the description below

  above relates to known glass furnace structures and is merely given as an example. Lost gases from the furnace, preheated combustion air from the furnace, or additional atmospheric air that has been previously heated

  appropriately, can be used to

  the vitrifiable mixture preheater.

  According to the present invention, a preheater i1 is mounted at a point adjacent to the vitrifiable batch inlet end of the glass melting furnace at a height greater than the normal height of the vitrifiable batch loading devices 12 that the furnace comprises. . The glass forming ingredients are brought into a suitably mixed state, at the top of the preheater 11 by any

  suitable means, such as a vertical elevator 32.

  The vertical elevator may be constituted by an arrangement of

  endless chain or bucket type having an ordinary structure

  and able to take from a stack or hopper the

  mixture of glass formation and deliver it into a gou-

  monkfish through which this mixture reaches the summit of the

  11. The glass forming mixture comprises normal constituents mixed with a vitrifiable furnace and may

  optionally contain milled cullet to form the glass bath.

  The size of the cullet corresponds to a US sieve size of between about 12.7 mm and 25.4 mm, the smallest size being preferred for passage through

  the preheater to prevent agglomerate clogging

  tion. The preheater typically comprises a vertical chamber 13 having a rectangular cross-section with a frustoconical upper cover 14. The main mass of the vitrifiable mixture is discharged via a chute 15 into the lower region of the vertical elevator.

  32 to be unloaded in the upper part of the pre-

  driver 11. Between the closed top cover and the

  of the main body of the preheater is found ume plate superior

  inner horizontal 16 in which are implanted,

  at their upper ends, numerous tubes 17 at the end

  The sone tubes are mounted in a spaced apart, parallel and vertical arrangement in response to the passage of the vitrifiable mixture. The tubes have an inside diameter of approximately c and extend over the entire central portion of the

  preheater to an inner horizontal lower plate

  18 in which they are implanted in a similar manner.

  The central portion of the preheater thus comprises a casing and an arrangement of tubes. The number of tubes and the dimensions of the preheater depend on the dimensions of the melting furnace.

  glass with which these tubes are used, as well as

  intended use. The tubes are mounted with a spacing of approximately 15.2 to 20.3 cm if tubes with an internal diameter of 10.2 cm are used, the tubes at the corners being usually omitted if the preheater has a rectangular horizontal cross-section. or square. The tubes are preferably made of stainless steel or carbon steel for prolonged use without rust or corrosion and are normally equi-distant for optimum flow.

batch batch mixture.

  The lower region of the preheater comprises a lower truncated pyramid hopper in which the open-ended tubes 17 pour out the vitrifiable mixture.

2489Z95

  heated. The lower hopper ends at its lower end.

  The diverting valve comprises at its outlet a Y-shaped portion for directing the main part of the chamber. vitrifiable mixture heated to a glass batch batching device 24 via a chute 23. The vitrifiable batch loading device can discharge the vitrifiable mixture heated in the oven 10 via a delivery element screwless

  end or any other means known in the art.

  Immediately above the lower inner plate 18 of the preheater is mounted an incoming gas conduit 25 for discharging very hot lost gases into a lower region of the preheater. The duct is designed from

  way to lead into a wide and relatively

  flat, with a width comparable to that of preheating

  In order to introduce the very hot gases over the entire width thereof, immediately below the upper inner plate 16 of the preheater, is mounted a conduit 26 of outgoing gas lost to evacuate the very hot lost gases. 'an upper region. The conduit is constituted by an output of

  wide and relatively flat duct whose width is comparable

  to the preheater to evacuate very hot gases

over its entire width.

  A plurality of flat baffle plates 27 are mounted in a staggered arrangement spaced apart from each other within the preheater between the upper, and lower, inner plates 16 and 18. The baffle plates 27 have openings through which the tubes 17

  extend between their upper and lower ends.

  The baffle plates can direct the very hot lost gases flowing upward along a sinuous path for turbulence to be communicated to the gases and thereby obtain better heat transfer to the tubes and the mixture. vitrifiable moving down by gravity

inside these.

  The batch is progressively and continuously

  naked through the preheater from its top up

  its base. It is then discharged by being heated in a single

  form and being perfectly mixed, the lower hopper of the preheater in the vitrifiable batch loading device 24 that includes the oven. The vitrifiable mixture is thus advanced in a slow and centinue manner towards the ba into the furnace zone in the course of its fusions. The vitrifiable mixture in the preheater is indirectly heated by the very hot lost gases which are taken from the furnace before their arrival. at the fireplace. As can be seen, the very hot gases enter the lower region of the preheater near the lower end of the tubes and above the bottom plate 18, the gases passing through.

  then along a winding path around the china plates

  cane 27 to the top of the preheater at the location of a

  The inlet and outlet conduits 25 and 26 may be provided with registers so that the flow of the very hot gases through the preheater can be regulated. precisely. The gases flowing countercurrently up to

  glass forming materials in the process of

  the tubes, move between and around these tubes by heating them and, indirectly, the batch they contain. In addition, the hottest gases act

  therefore on the hottest parts of the constituents of

  in the lower zone of the preheater, which further increases the heat of this part before it

  does not arrive in the melting furnace. As mentioned above,

  above, the hot gas stream may be lost gases from the furnace heating zone or by preheated air from the furnace stack region, or preheated outside air which has been heated further before being supplied to the preheater of

vitrifiable mixture.

  Thanks to an appropriate design of the upper and lower hopper sections of the preheater, these sections generally having the shape of pyramid trunks, a relatively uniform and regular flow of the materials of the pyramid is obtained.

  vitrifiable mixture over the entire height of the preheat

  feur. Thus, for uniform amounts of preheating heat, flow rates of the vitrifiable mixture are obtained through

  all the tubes of the heat exchanger that hold those

  practically full at all times. The preferred embodiment is one having a straight section with rounded corners in an upper region above the

  tubes, and a wedge-shaped hopper whose corners are rounded

  at the bottom ends of the tubes for a continuous displacement of the vitrifiable batch dry and very hot * Sufficient pressure is thus maintained above the tubes to ensure -this flow, at the same time is provided a drive device suitable for evacuating the material

  preheated from the base of the hopper.

  The diverting valve 22 serves to separate the vitrifiable batch stream flowing downward into a main part and a secondary part. The main part is discharged into the vitrifiable batch loading device 24 via a chute 23, while the secondary part is discharged into a gong 30 where it is mixed with a cold batch mixture coming from the source of the batch. food. The vitrifiable mixture comprising the very hot fraction and the cold fraction is then conveyed down to the base of the vertical conveyor 32 which serves to raise the batch and discharge it into the part

  upper preheater through inlet chute 33.

  Through a choice of proper proportion and a perfect blend of the very hot and recycled blend fraction

  vitrifiable and cold fraction and newly introduced

  batch of batch, we can get a functioning

  uniform and continuous preheater. This result can be obtained

  when the temperature conditions and the flow of the gases and the material of the batch have been adjusted appropriately. Such uniform operation makes it possible

  keep warm conditions inside the preheater.

  consistent furnace to provide a considerably warmer vitrifiable batch in the furnace, significantly increasing the efficiency of this furnace. The temperature of the stack gases entering the furnace

  Preheater varies of course with the condition; in the-

  what is the oven; however, it is normally between 48200 and 5990C and frequently reaches an average value of about 543C for significant periods. The temperature of the gases leaving the preheater is between 204 00 and 316 C0,

  and their average temperature is about 26,000.

  Of course, additional heating means may be provided for the preheater, if desired, although the lost gases from the furnace are usually perfectly suitable for the most economical operation. The lost gases or the very hot air normally enter the furnace. preheater at a temperature between about 482 C and 5990C, after leaving the combustion zone or the stacking zone of the oven. As mentioned, the preheated combustion air that has passed through the furnace heat recovery zone can also be used to heat the vitrifiable mixture in the preheater, or a source of heat can be used.

  separate additional heat such as a burner.

  The lost gases, or the very hot air, normally leave the preheater at a temperature between about 204 C and

3160C0.

  The vitrifiable mixture usually enters the upper part of the preheater at a temperature of about 12 ° C. and leaves the preheater at the location of the diversion valve 22 at a temperature between 4270 ° C. and 53 ° C. The above temperatures can be reached with

  25 to 30 percent by weight of vitrified mixture.

  recycled. These temperatures are possible with an oven that is capable of producing about 240 tons per day of product. The present invention lends itself to continuous operation when the vitrifiable mixture in the cooler upper region of the preheater is maintained at room temperature.

  a temperature above the boiling point temperature

  water. If the temperature of the vitrified mixture is allowed to

  in this region to fall below the boiling point of the water, the residual moisture within the batch may condense inside the tubes as well as indoors.

  of the upper closure element 14 of the preheater

  vooing a shutter of the tubes and an agglomeration of the mass which is normally fluid. This shutter prevents optimal operation of the preheater and is intolerable in long-term operation. By keeping all the surfaces of the preheater which are in contact with the vitrifiable mixture at a temperature above the dew point temperature or at the boiling point temperature of the water contained in the vitrifiable mixture, adhesion can be prevented. of this mixture to the contact surfaces and one can

maintain a steady flow.

  The present invention is not limited to the interaction of a single preheater with a single melting furnace, the first being in communication with very hot gases resulting in a single stack. If desired, it is possible to connect a single preheater so that it serves several melting furnaces, or one can associate several preheaters with a single

  oven and direct on them the lost gases emitted by the latter.

  The present invention can also be used for heating individual vitrifiable batch components such as sand, lime, sodium carbonate, etc., to remove moisture therefrom before introducing them into a melting furnace, for example . In addition, ealcin, or mixtures of

  vitrifiable charges and cullet, in very

  The particulate material may also be heated in the apparatus and using the process of the invention, provided that the particulate material contains one or more volatile components that tend to condense within the heater. Such constituents of mixtures or vitrifiable charges may be

  heated individually or combined to temperatures of

  eratures between 3150C and 42700C. The cullet, when heated alone, can be brought to temperatures even

higher.

  The batch or batch and mixture thereof may be heated by recycling a weight by weight.

  up to about 70% -more cullet this recycling emp $ -

  This closes the tubes in the zones of the tubes which are made colder by condensation of moisture. In practice, all zones of the zones, and especially their upper zones, are maintained at a temperature higher than the boiling point temperature of the water, that is to say

  100LC. The particulate material to be heated may

  keep a volatile component, such as water, or a decomposable constituent that produces water when it decomposes. Such constituents can be easily removed by heating without interrupting the continuous flow of the particulate material through the heater under the effect of

gravity.

  It is understood that the foregoing description has not

  given merely as an illustration and not as a limitation, and that variations or modifications may be made

  in the context of the present invention.

Claims (22)

  1. A process for preheating a vitrifiable mixture before it is transferred to an oven for melting the glass,   characterized by the fact that it consists in introducing the con-   fully mixed components of the batch in the   upper region of a tubular heat exchanger, to be   the batch can flow downward by gravity through a plurality of open ended tubes of said heat exchanger, passing very hot gases upwardly through said heat exchanger around said open ended tubes; to heat the batch mixture contained in these tubes by an indirect heat transfer and against the current, to separate from the main part of the vitrifiable mixture heated a secondary part into a   adjacent to the base of said heat exchanger and to   sensing said secondary portion in the upper region of said heat exchanger for recycling, and transferring the main portion of said vitrifiable mixture from the base   said furnace heat exchanger for melting the glass.   Process according to Claim 1, characterized in that very hot gases from said glass melting furnace are directed upwardly in a sinuous and countercurrent path around said open ended tubes by a series of baffles. spaced so that a   greater indirect heat transfer is obtained.   3. Process4 according to claim 1, characterized in that a secondary portion equal to about one third of the mass of the vitrifiable mixture is recycled through said heat exchanger so as to eliminate the condensation of the residual moisture at the inside or above said tubes by maintaining the temperature of the vitrifiable mixture passing through said heat exchanger above the point boiling water.   4. Process according to claim 1, characterized in that the secondary part of said vitrifiable heated mixture is directed by a diversion valve located at a point adjacent to the lower region of said heat exchanger.   heat to a vertical elevator for recycling.   5. Method according to claim 1, characterized in that the main part of said vitrifiable heated mixture is diverted to a glass batch batching device communicating with said glass melting furnace, the aforementioned diversion being carried out by a diverting valve located at a point adjacent to the lower region said heat exchanger.   6. Process according to claim 1, characterized in that the batch is kept inside said heat exchanger at a temperature above the boiling point temperature of the residual moisture. said batch vitrifiable.   7. Process according to Claim 1, characterized in that the said vitrifiable mixture is heated to a temperature of between approximately 4260C and 5380C in order to supply the said main part to the said glass melting furnace and to recycle the said secondary part into the said heat exchanger. 8. A method according to claim 1, characterized in that the secondary part of said vitrifiable mixture is sent to an upper region of said heat exchanger   under an inlet temperature greater than 1000C.   9. A method according to claim 1, characterized in that said batch vitrifiable through open end tubes that includes said heat exchanger and   whose uniform inner diameter is about 10 cm.   10. Apparatus for preheating a vitreous mixture   reliable for a glass melting furnace, characterized by   the fact that it includes a vertical mounted heat exchanger-   and an elongate shape having a multiplicity of open ended tubes extending throughout a major part of the height of this exchanger, means for transferring batch batch batching to the fully mixed state in an upper region said heat exchanger for gravity passing through said end tubes   opened, a means of introducing very hot gases   said glass melting furnace in a lower region of said heat exchanger so as to circulate   between said open-ended tubes, a means for   mant chicane mounted around said tubes so as to direct   said hot gases along a sinuous path around the   said tubes and without being in contact with said vitreous mixture   reliable for indirect heat transfer, and means for separating a secondary part of said mixture from the main part of said vitrifiable mixture and for returning said secondary part to said upper region of said heat exchanger, the main part of said vitrifiable mixture being transferred to a mixture loading device   vitrifiable that includes said glass melting furnace.   He. Apparatus according to claim 10, characterized in that said means for introducing said hot gases into a lower region of said heat exchanger.   heat includes a duct extending from the chamber of com-   furnace bustion jusqutaudit heat exchanger.   Apparatus according to claim 10, characterized   in that said means for separating a secondary portion   said vitrifiable mixture comprises a diverting valve   is lying. 13. Apparatus according to claim 10, characterized in that said baffle means comprises a series   of baffle plates extending horizontally in a   alternating position and being spaced from each other in the form of a row inside said heat exchanger   around said open ended tubes.   14. Apparatus for preheating the constituents of a vitrifiable mixture, characterized in that it comprises a glass melting furnace, a conduit for conveying the very hot gases from this furnace, an elongated preheater for preheating the components of the vitrifiable mixture and mounted vertically at a point adjacent to said glass melting furnace at a height greater than that of said furnace, open ended tubes extending through the main central portion of said preheater for   gravity conveyed said vitreous mixture constituents   reliable, said conduit being connected to a lower region of said preheater to introduce the very hot gases therein for their upward passage around said tubes, a chicane means weai @ a-turn desdi- tubes for directing said lost gas very hot ato'ur of the latter   following a sinuous route and against a backdrop   indirect heat generation to said vitrifiable mixing constants, and means for separating a main amount.   and a secondary amount of the constituents of the vitreous mixture.   reliable heating in a lower region of said preheater, -   the secondary amount being returned to a higher region   said preheater for recycling through this pre-heater.   driver and the main quantity being supplied to a   vitrifiable batching device comprising said glass-melting furnace, Apparatus according to claim 14, characterized   in that said baffle means comprises a plurality of   a plurality of flat plates extending horizontally in an alternating arrangement and spaced apart from each other within said preheater around said open ended tubes to provide a sinuous and countercurrent flow of gas 16, next apparatus claim 14, characterized in that said open ended tubes generally have a uniform length and an inside diameter   uniform that is not less than 5 cm.   17. Apparatus according to claim 14, characterized in that said means for separating a main quantity and a secondary amount of constituents of the vitrifiable heated mixture comprises a diverting valve placed in the immediate vicinity of the lower region of said preheater. 18. Apparatus according to claim 14, characterized in that said elongate shaped preheater has a rectangular cross-section and the open ended tubes are vertically arranged equidistantly spaced apart in a casing-tube arrangement for conveying down by gravity said constituents of the vitrifiable mixture.   A method of heating a particulate material such as a batch, individual components of a batch, cullet, a mixture thereof, and the like, which contain a volatile component capable of condensing, characterized in that it consists in introducing the particulate material into the upper region of a long and vertically mounted tubular heat exchanger, allowing the particulate matter to flow downward by gravity through a multiplicity of tubes. with open ends that includes said heat exchanger, to pass very hot gases up to,   through said heat exchanger around said end tubes   Opened to heat the particulate matter contained therein by indirect and countercurrent heat trails, to separate from the main portion of the particulate matter heated a secondary portion adjacent to a region lower part of said heat exchanger, to return said secondary part in the upper region of said heat exchanger for its recycling, eth to evacuate from the lower region of said heat exchanger the main part of said particulate material in a heated state substantially free said volatile constituent likely to condense.   20. Process according to claim 19, characterized in that a secondary part equal to about one third of the mass of the particulate material is recycled in said heat exchanger to eliminate residual condensation.   of moisture inside or above said tubes while maintaining   particulate material passing through said heat exchanger at a temperature above the boiling point of water. 21. Process according to Claim 19, characterized   in that the secondary part of the said material in part   particles is returned to an upper region of said exchanger   of heat under an inlet temperature of about 1000C.   22. The method of claim 19, characterized   in that said particulate material passes through a multi-   of open-ended tubes contained in the said sample   heat and has a uniform inner diameter about 10 cm.   23. The method of claim 19 characterized in that said particulate material is heated to a temperature between about 4260C and 5380C   for the transfer to a melting furnace of the main part of   blade of said material in particular and recycling of said   secondary part in said heat exchanger.   24. The method of claim 19, characterized   in that the particulate matter is maintained in the   said heat exchanger at a temperature above the boiling point temperature of the residual moisture of said particulate material.   Process according to Claim 19, characterized in that very hot gases are directed from a glass melting furnace upwards in a sinuous and countercurrent path around said open ended tubes by a series of spaced baffles. so that a transfer of   greater indirect heat is obtained.   A heat exchanger for heating a particulate material such as a batch, individual components of a batch, a mixture thereof, and the like, which contain a volatile component capable of condensing, characterized in that it comprises a long vertically mounted closed chamber with a multiplicity of open ended tubes extending over a whole main part of the height.   this room, a means of transferring the material in parti-   in an upper region of said heat exchanger in   view of its passage by gravity through said end tubes.   open-ended means for introducing very hot gases into a lower region of said heat exchanger so that they flow upwardly between said open-ended tubes, a baffle means mounted around said tubes between their ends so as to direct said hot gases in a serpentine path around said tubes and not in contact with said particulate material for indirect heat transfer, and means for separating from the   main part of the particulate matter heated a part   of a lower region of that sample   heat generator, means for returning said secondary portion to the upper region of said heat exchanger, and means for discharging the main portion of said particulate material to a lower region of said heat exchanger in a heated state, substantially free of said component   volatile that can condense.   27. Heat exchanger according to claim 26, characterized in that said baffle means comprises a series of baffle plates extending horizontally in an alternating arrangement being spaced from each other   in the form of a vertical row, within the said   heat gap around said open ended tubes.   28. Heat exchanger according to claim 26, characterized in that said means for separating a secondary portion of said particulate material comprises a diverting valve.   29. Heat exchanger according to claim 26, characterized in that said means for introducing very hot gases into a lower region of said heat exchanger comprises a duct extending from a melting furnace to said heat exchanger. 30. Heat exchanger according to claim 26, characterized in that said means for returning said secondary portion of the particulate material heated in the upper region of said heat exchanger comprises   a bucket elevator6 and connecting ducts.   31 * Heat exchanger according to claim 26 ,.   characterized in that said open ended tubes generally have a uniform length and a diameter   uniform interior that is not less than about 5 cm.   32. Heat exchanger according to claim 26, characterized in that said long closed chamber has a rectangular cross-section and that the open-ended tubes are arranged vertically and equidistantly in an envelope-tube arrangement intended to transport downwards. by gravity matter in particles *